The present invention relates to a pressurized vessel for storage of hydrogen in the form of metal hydride, and more particularly, the invention relates to a pressurized container with a cylindrical jacket, end caps, and a storage medium which, on charging, will produce hydride.
There have to be included suitable conduits for feeding and discharge of hydrogen, moreover, is is practical to provide the cylindrical part of the container in a two or twin-wall configuration, the two walls being separated by bars, separating individual flow channels, along which a heat exchange medium flows during hydration and dehydration.
Broadly speaking, a pressurized container of the type to which the invention pertains, is known through German printed patent application No. P 35 02 311. Herein, the outer surface of the container is essentially formed through a circular cylindrical jacket whose axial ends, or front ends, are closed, for example, through spherically shaped end caps. The hydride forming metal alloys store hydrogen in the interior of the vessel, in that during storage and gas feeding hydride is being formed. The bonding enthalpy releases heat which has to be discharged in some fashion in order to obtain, at a given load pressure, the largest possible gas storage. On the other hand, for unloading the storage facility it is necessary to feed heat to the metal hydride so that, indeed, hydrogen can be released which is an energy consuming process.
In order to obtain a high utilization factor of the storage facility it is desirable to load and/or unload the facility in as short as possible a period of time commensurate with a very high gas throughput. This in turn requires a fast heat exchange process between a medium charge which flows in heat relation with the interior of the vessel. In order to improve that heat flow and transfer, it is known to increase the effective surface through ribs, as is customary for heat exchanges to thereby increase the heat transfer in one direction or the other as between heat exchange medium, on one hand, and container wall, on the other hand.
Another kind of hydrogen storage facility is known to have a plurality of parallelly arranged and interconnected longitudinal containers of relatively small diameter, such as 30 mm, so as to obtain a bundle of individual containers, which are then, in turn, placed in a common housing. The heat exchange medium is, in this case, fed into the common housing and flows in the interspaces between the individual containers within that housing. These individual containers have a smooth surface.
This configuration has the advantage that upon dividing the facility into small individual storage facilities, one increases effectively the surface area available for heat exchange. Moreover, one has available, in fact, a heat exchange process that penetrates the vessel throughout, and is thus based only on comparatively short heat transfer paths. On the other hand, it was found that this arrangement was quite expensive and requires an extensive assembly procedure.
In order to increase the storage facility and capacity, it is often desirable to provide the hydride storage facility with a load and unload pressure that is quite high. This, of course, entails a container wall to be very strong. Usually stainless steel is used here because it is also necessary to protect the vessel against corrosion and agression of the hydrogen. On the other hand, stainless steel is a very poor heat conductor and, thus, opposes the process of a fast heat exchange.
The Japanese Patent No. 59-146,902A describes a twin wall hydride storage facility while the inner container is made of copper or aluminum which is a good heat conductor. In addition, ribs extend radially and axially parallel from that inner container towards the outer jacket, and thus constitute an intermediate flow space between the two jackets, or in-between the inner and outer vessel. The individual channels can be passed by a heat exchange medium. The ribs do indeed increase the area available for heat exchange between the container and the heat exchange medium, but this construction requires an unweakened wall of container material, and therefore, the wall has to be quite thick, and will simply take up large hydrogen pressure which then will impede the heat flow to and from the hydride jacket. On the other hand, if the walls are thin, the heat exchange is carried out fast but the operating pressure is too low.